There exists a large number of approaches to all-optical information processing devices. They fall in several categories depending on their applications. The largest current market is the telecommunication industry, which tries to anticipate future requirements to increase speed of the information processing by incorporating all optical devices that would not require transformation of signal from optical to electric form and back for the processing.
There is a need for devices that are wavelength selective as well as those that can manipulate with pulses containing many wavelengths. Some of the technologies directed to this market have already been commercialized. One can mention here micro-electro-mechanical-systems (MEMS) based devices, holographic optical switches, liquid-crystal-based switches, etc. Their speed is still limited, and therefore new ideas directed to improving this characteristic are being developed.
Among new approaches, which are in the R&D stage and have not yet reached the stage of commercialization, are directed to improving speed and other characteristics, such as on/off ratio, modulation depth, band width, etc., of wavelength sensitive devices, and which include:                Waveguide-based optical switches and modulators.        Photonic-crystal-based all-optical devices.        MQW-based electro-optical devices.        
The first two on the list above are rather closely related to each other since they both exploit interference between light pulses separated and guided along two different channels. The interference can be influenced either by exploiting the natural non-linearity of the constituting materials or by inserting active elements, such as quantum dots whose properties can be changed by applying an electric field or by other ways. The difference between these two is their approaches to constructing waveguides-using more traditional internal reflection based waveguides or using photonic crystals for similar purposes.
The last of the devices listed above uses spectral region of exciton resonances for light transmission and quantum-confine Stark effect to control transmission at a given frequency. They are based, however, on MQW structures that drastically differ from embodiments of the present invention, and have therefore significantly different technological characteristics.
These existing approaches have the disadvantages of:                Low speed.        Difficulties in achieving tunability.        Lack of multi-functional capabilities.        
Thus, there exists a need for an all-optical device that is tunable and has high speed and multi-function capabilities.